Wrong forum dude, hahaha, go up a few and you'll see the Cyclura/Ctenosaura forum. many folks there own spinys, and will be of a much bigger help.
But, while I'm at it... 
Spinys are generally not as tame as iguanas, but there are exceptions, just as there are sometimes green iguanas who seem to come from Hell and don't really tame that much.
Spinys are a 'well-rounded' iguana, as in, they have a bit of everything: good for hot, dry climates (so they do not require as much humidity as greens, but still do a bit), they do not grow too big (3 feet is the average, 4 feet max), and their diet can include a small percentage of protein (even though that is debated). They look something in between a green and a cyclura, so they are nice looking iguanas!
However, just because they grow to be about 2 feet less than green iguanas, they still require an enclosure JUST AS BIG, so no shortcuts here.
They have a temper, and the spiny tail will really crack u good, better than a green's, so watchout once it will grow.
I have been told they are somewhat more "intelligent" than green iguanas, more inquisitive and more observant.
Their teeth are different from green iguanas, being sharper and more needle-like, hence indicating that hunting small prey (insects or whatever) may be in their diet.
Melissa Kaplan does mention some information on their husbandry, and I'm sure if you google around you'll find more info. Her book, as well as Hatfield's, can be applied to their care, since botrh animals are almost identical in captive care.
Patience and commitment are the key to have a good exotic pet.
$9.00 is a bargain, but make sure it will see immediately a Vet for de-worming etc.
Reason they're so cheap is because not a lot of people want them, being not as popular as iguanas, not as rare and particular as cycluras, or small and cute/easy to keep as desert iguanas (another great candidate). Also, they are probably wild-caught, sold in masses, most of them dying or getting sick with parasites... or it has been returned by a previous owner, and now sold at a discount.
Mexicans spinys from what I remember are the bigger ones and look pretty darn cool. Baby spinys are green, and then change colors. Spiny taileds are also called 'club-tailed' iguanas.
I think you'll get great info from the folks in the other forum, since they are owners and will be able to give you personal experiences etc.
Let us know if you get it.
I'd say Spinys are like Monitor lizards in temper and wit, again, from what I have heard. But there are always exceptions, so think it through.
-IJ